Camshaft vs Crankshaft Position Sensor Testing Methods

Your engine has two sensors that keep everything running in sync the camshaft position sensor and the crankshaft position sensor. When one fails, you get misfires, stalling, rough idle, or a no-start condition. But here's the tricky part: both sensors can throw similar trouble codes and cause overlapping symptoms. Knowing how to test each one separately can save you hundreds in diagnostic fees and hours of guesswork. This article walks through the real testing methods mechanics use, so you can figure out which sensor is actually the problem.

What's the Difference Between a Camshaft and Crankshaft Position Sensor?

Before you grab a multimeter, you need to know what each sensor does. The crankshaft position sensor (CKP) monitors the position and rotational speed of the crankshaft. The engine control module (ECM) uses this signal to control fuel injection timing and ignition spark. Without it, most engines won't start at all.

The camshaft position sensor (CMP) tracks the position of the camshaft, which tells the ECM which cylinder is on its compression stroke. This is especially important for sequential fuel injection systems. A failed cam sensor might still let the engine run in a "limp" mode, though performance will suffer.

Both sensors work together. The ECM compares their signals to verify valve timing is correct. If one signal drops out or becomes erratic, the other can't compensate alone. That's why testing both matters, even if a code points to just one.

What Tools Do You Need for Testing?

You don't need a full shop to test these sensors. Here's a short list of what works:

Digital multimeter for checking resistance, voltage, and signal output
OBD-II scanner to pull freeze-frame data and live sensor readings
Oscilloscope (optional) for viewing waveform patterns in real time
Basic hand tools wrenches or sockets to remove sensors if needed

For most DIY diagnostics, a multimeter and an OBD-II scanner cover 90% of what you need. If you want a deeper look at scanner-based diagnosis, we cover how to use an OBD-II scanner for camshaft sensor diagnosis in a separate walkthrough.

How Do You Test a Crankshaft Position Sensor?

Resistance Test (Most Common DIY Method)

This is the go-to starting point. Here's how it works:

Disconnect the CKP sensor connector.
Set your multimeter to the ohms (resistance) setting.
Place the probes on the two sensor terminals.
Compare the reading to your vehicle's service manual spec typically between 200 and 1,000 ohms, depending on whether it's a Hall-effect or magnetic reluctance type.

A reading of infinite resistance (open circuit) or near zero (shorted) means the sensor is bad. If the resistance falls within spec, the sensor windings are intact but that doesn't guarantee the sensor is producing a clean signal under operating conditions.

Voltage Output Test

With the sensor connected and the engine cranking (but not started), set your multimeter to AC voltage. A healthy magnetic-type CKP sensor should produce 0.5 to 1.5 volts AC while cranking. No voltage means the sensor or its wiring has failed.

Waveform Test with an Oscilloscope

A scope shows you the actual signal pattern. A good crank sensor produces a consistent, evenly spaced waveform. Irregular gaps, flatlines, or erratic spikes all point to problems either with the sensor itself or with the reluctor ring it reads.

A thorough breakdown of resistance testing on the cam side is available in our guide to DIY camshaft position sensor resistance testing with a multimeter.

How Do You Test a Camshaft Position Sensor?

Resistance Test

The process mirrors the crank sensor test:

Unplug the CMP sensor.
Measure resistance across the terminals with a multimeter.
Typical specs range from 200 to 900 ohms, but always check your specific vehicle's manual.

Out-of-range readings mean the sensor needs replacement. In-range readings suggest the sensor coil is fine, but wiring or signal issues could still exist.

Voltage Backprobe Test

With the sensor plugged in and the engine running, backprobe the signal wire. You should see a pulsing voltage that changes with engine RPM. On Hall-effect cam sensors, expect a switching signal between 0V and 5V. On magnetic types, you'll see an AC voltage that increases with engine speed.

OBD-II Live Data Method

A scanner with live data capability can show you cam sensor readings without touching the wiring. Look for:

RPM signal that matches engine speed
Signal status toggling between "active" and "inactive"
Correlation with the crank sensor signal

If the ECM flags a P0340 (camshaft position sensor circuit malfunction) or P0335 (crankshaft position sensor circuit malfunction), live data helps you confirm whether the sensor is truly dead or if the issue is intermittent. For a full breakdown of both sensors' testing approaches, see our complete comparison of camshaft and crankshaft sensor testing methods.

Which Trouble Codes Point to Which Sensor?

Knowing the codes narrows things down fast:

P0335 – P0339 Crankshaft position sensor circuit issues
P0340 – P0349 Camshaft position sensor circuit issues
P0016 – P0019 Correlation errors between cam and crank signals (often a timing chain issue, not a sensor)

A correlation code (P0016 family) doesn't always mean a sensor is bad. It can indicate a stretched timing chain, jumped timing, or a worn reluctor ring. Always test the sensors before replacing parts based on codes alone.

What Are the Most Common Testing Mistakes?

Even experienced DIYers make these errors:

Replacing a sensor based only on a code. Codes tell you there's a circuit problem, not necessarily a failed sensor. Wiring, connectors, and even the reluctor ring can trigger the same code.
Not checking the air gap. Both sensors need to sit at the correct distance from the reluctor ring. A sensor mounted too far away even by a fraction of a millimeter can produce weak or no signal.
Ignoring the wiring harness. Chafed wires, corroded pins, and loose connectors cause more sensor "failures" than dead sensors do. Always inspect the harness first.
Skipping the reluctor ring inspection. A cracked, missing-tooth, or corroded reluctor ring will fool a good sensor into producing bad data.
Confusing the two sensors. On some engines, the cam and crank sensors look identical. Installing them in the wrong location creates a no-start condition and a head-scratching diagnostic loop.

Can You Test Without Removing the Sensor?

Yes, and in many cases that's the better approach. Backprobing with a T-pin or a breakout harness lets you measure voltage and signal output while the sensor stays installed. OBD-II live data is another non-invasive method. Removing the sensor risks damaging the O-ring, the connector, or the mounting bore especially on older vehicles where corrosion has set in.

That said, a bench resistance test after removal is more precise. If you suspect the sensor is marginal, pulling it for a direct measurement removes any doubt about wiring or connector issues skewing your reading.

How Do the Two Sensors Compare Side by Side?

Here's a quick reference:

Function: CKP tracks crankshaft rotation; CMP tracks camshaft rotation
Engine behavior if failed: CKP failure usually causes a no-start; CMP failure often allows limp-mode operation
Resistance range: Both typically 200–1,000 ohms (varies by vehicle and sensor type)
Common codes: P0335 family for crank; P0340 family for cam
Testing methods: Resistance, voltage output, waveform, and OBD-II live data all work for both
Typical cost to replace: $15–$75 for the part; $100–$250 for professional installation

When Should You Replace Instead of Test?

If the sensor has visible damage melted housing, broken connector, oil saturation inside the sensor body don't bother testing. Replace it. Sensors that have been submerged in oil from a leaking valve cover gasket often fail intermittently, which makes them frustrating to diagnose. Replacing both the gasket and the sensor at the same time is usually the smarter move.

Also, if you've confirmed the sensor is bad through testing and your vehicle has over 100,000 miles, consider replacing both the cam and crank sensors. They're both wear items, and the labor to get to either one often overlaps. You save time by doing both at once.

Practical Testing Checklist

✅ Pull codes with an OBD-II scanner before touching anything
✅ Visually inspect both sensor connectors and wiring for damage
✅ Check resistance on both sensors and compare to factory specs
✅ Backprobe signal wires with the engine running to verify output voltage
✅ Use live data to confirm cam-crank signal correlation
✅ Inspect the reluctor rings if sensors test good but codes persist
✅ Verify correct air gap after reinstalling or replacing a sensor
✅ Clear codes and road test to confirm the repair before closing everything up

Next step: If you've narrowed the problem to the cam sensor and want to do a hands-on resistance check, start with a multimeter and our step-by-step resistance test guide. If you'd rather use a scanner, our OBD-II scanner diagnosis walkthrough covers live data interpretation in detail. Either way, test before you replace it's the fastest path to the right fix.

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